FIG. 1 illustrates a wind turbine 1, comprising a wind turbine tower 2 on which a wind turbine nacelle 3 is mounted. A wind turbine rotor 4 comprising at least one wind turbine blade 5 is mounted on a hub 6. The hub 6 is connected to the nacelle 3 through a low speed shaft (not shown) extending from the nacelle front. The wind turbine illustrated in FIG. 1 may be a small model intended for domestic or light utility usage, or for example may be a large model, such as those that are suitable for use in large scale electricity generation on a wind farm. In the latter case, the diameter of the rotor may be as large as 100 meters or more.
When selecting a wind turbine for a given operating location, consideration is given to the characteristics of the site such as the complexities of the site terrain and the average wind conditions. The turbine chosen can ideally operate at rated power for as much of the time as possible. However, in practice, wind speeds are variable and the turbine must be able to cope with a wide variety of wind speeds. At lower wind speeds the power output will either be zero, if there is negligible wind, or below rated power. Once the wind speed increases to above that required for rated power the turbine will protect itself from damage, for example, by varying the pitch of the blades to reduce the power extracted from the wind. In extreme cases the turbine may shut down or yaw out the wind to prevent catastrophic damage.
When adjusting the pitch angle to compensate for changes in wind speed measured at the wind turbine, there is an inevitable time delay between the detection of the instantaneous wind speed detection and the blades being brought into the correct pitch position. It is therefore known to control the pitch of the wind turbine based on the future expected wind speed measured using a LIDAR apparatus.
The use of LIDAR to control operation of wind turbines is known, for example, from U.S. Pat. No. 6,320,272 of Lading et al, which teaches the use of a laser wind velocity measurement system such as a LIDAR (Light Detection and Ranging) apparatus mounted on the nacelle. LIDAR operates by emitting a laser beam in front of the wind turbine to measure the conditions at a distance in front of the wind turbine. The distance is typically arranged to be between 0.5 and 3 rotor diameters away from the turbine, which is therefore in the order of 50 to 300 m for a large modern wind turbine. LIDAR operates in known manner either by detecting air molecules or by detecting particles entrained in the air stream and calculating information about the air flow from these measurements. This information may include wind speed and direction and wind shear in the vertical and horizontal directions although the parameters that can be calculated will depend on the complexity of the LIDAR used. The pitch angle can then be adjusted in advance of changes in wind speed and the operation of the wind turbine can subsequently be made more efficient.
However, adjustment of rotor blade pitch based on measurements of the future value of the wind can lead to other operational difficulties, such as how control based on those variables is to be performed in real time for a wind turbine generator. In this regard, we have appreciated that there is a need for an improved control technique.
Furthermore, real time control of the wind turbine to adjust mechanical or electrical control parameters can lead to increased wear and tear on the control actuator system if the control is not performed properly. We have also appreciated that control of the wind turbine based on the predicted value of future parameters can be used to offer a more reliable and more responsive control system.